Prostaglandins are important mediators of inflammation and are also involved in a cytoprotective role in gastric mucosa. Of particular interest in the present application are the prostaglandin producing enzymes COX-1 and COX-2, also known as prostaglandin H synthase-1 (PGHS-1) and prostaglandin H synthase-2 (PGHS-2). COX-1 is the constitutive isoform and is mainly responsible for the synthesis of cytoprotective prostaglandins in the GI tract whereas COX-2 is inducible and plays a major role in prostaglandin biosynthesis in inflammatory cells and in the central nervous system. Considerable research has been conducted to isolate therapeutic agents which are specific for the inhibition of COX-2, i.e. agents which have the anti-inflammatory benefit of COX-2 inhibition without the GI tract irritation associated with inhibition of COX-1; see, for example, Vane et al., 1998, Annual Rev. Pharmacol. Toxicol., 38:97-120; Masferrer et al., 1994, Proc. Natl. Acad. Sci., 91:3228-3232; Vane et al. 1995, Inflamm. Res. 44:1-10; Seibert et al., 1994, Proc. Natl. Acad. Sci., 91:12013-12017; and Dubois et al., 1998, The FASEB Journal, 12:1063-1072.
Previous research indicates that COX inhibitors can have different selectivity ratios if profiled in assays using cells from different species or sources and it has been postulated that some classes of inhibitors may be species specific in nature; see, for example, Ricketts et al., 1998, AJVR 59:1441-1446, Warner et al., 1999, Proc. Natl. Acad. Sci., 96:7563-7568, Laufer et al., 1999, Inflamm. Res., 48:133-138, Giuliano et al., 1999, British J. Pharmacol., 126:1824-1830, Riendeau et al., 1997, Can. J. Physiol. Pharmacol., 75:1088-1095, Khan et al., 1998, Toxicologic Pathology, 26(5): 612-620, and Golden et al., 1999, Osteoarthritis, 25(2):359-378. Therefore, isolation and sequencing of canine COX-1 and COX-2 genes may be critical for use in identifying COX-2 specific inhibitors specifically for use in dogs.
Thus, there remains a need to develop COX-2 specific therapeutic agents for use in dogs as well as reagents and methods to identify such therapeutic agents.